Shape memory materials such as nickel titanium (NiTi) alloys are promising materials for surgical implants in orthopedics due to their unique shape memory effect (SME) and super-elasticity (SE) that other common orthopedic materials such as stainless steels and titanium alloys do not possess. Their mechanical properties are also closer to that of cortical bones than stainless steels and titanium alloys. The materials display superior wear resistance to CoCrMo alloys used in bone trauma fixation. Several other favorable properties of the materials have also been investigated, and good bio-compatibility has also been reported. However, some negative effects have also been pointed out. For example, Berger-Gorbet et al. have found that the osteogenesis process and osteonectin synthesis activity in NiTi alloys are unfavorable compared to stainless steels and titanium alloys.1 Jia et al. in their study revealed that the cell death rate was severe on NiTi alloys.2 
These problems are believed to stem from the poor corrosion resistance of the materials, which may lead to an increase in their cytotoxicity. It is most likely that some toxic components released from the substrate cause the cell death rather than the apoptosis.3 Shih et al. reported that the supernatant and corrosive products from NiTi may result in the death of smooth muscle cells, especially when the amount of released nickel is higher than 9 ppm.4 A few other studies have also reported that nickel ions5,6 leached from the alloys cause allergic reactions in nickel hyper-sensitive patients.7-10 While the homogeneity of the materials microstructures and the surface morphology may alter the anti-corrosion ability of NiTi alloys, there is no doubt that the corrosion resistance and anti-wear properties of the materials must be enhanced before the materials can be widely used clinically, especially as orthopedic implants with couplings where fretting is expected.
Titanium carbides and nitrides have excellent mechanical and chemical properties, for example, good wear resistance, inactive with numbers of chemical substances and outstanding hardness [11-16]. Titanium oxides are known to be fairy compatible with living tissues [17-20]. They are also inactive to many chemical reactions. In surface coating industries, these elements have been applied to improve the mechanical and corrosion properties of the substrates through various methods [21-25] for a period of time.